COMPLEMENTAL AIE. 401 



and is not sufficiently marked to produce any sensation, such 

 as is experienced when respiration is in the slightest degree 

 interrupted. 



Tidal, or Ordinary Hreathing Air. The volume of 

 air which is changed in the ordinary acts of respiration is 

 subject to immense physiological variations, and the respira- 

 tory movements, as regards intensity, are so easily influenced 

 by the mind, that great care is necessary to avoid error in 

 estimating the volume of ordinary breathing air. The esti- 

 mates of Herbst and of Hutchinson are the results of very 

 extended observations made with great care, and are gener- 

 ally acknowledged to be as nearly accurate as possible. As 

 a mean of these observations, it has been found that the 

 average volume of breathing air, in a man of ordinary stat- 

 ure, is 20 cubic inches. According to Hutchinson, in perfect 

 repose, when the respiratory movements are hardly percep- 

 tible, not more than from 7 to 12 cubic inches are changed ; 

 while, under excitement, he has seen" the volume increased to 

 Y7 cubic inches. Of course the latter is temporary. 1 Herbst 

 noted that the breathing volume is constantly increased in 

 proportion to the stature of the individual, and bears no defi- 

 nite relation to the apparent capacity of the chest. 



Complemented Air. The thorax may be so enlarged by 

 an extreme voluntary inspiratory effort, as to contain a quan- 

 tity of air much larger than after an ordinary inspiration. 

 The additional volume of air thus taken in may be estimated 

 by measuring all the air which can be expelled from the 

 lungs after the most profound inspiration, and deducting the 

 sum of the reserve air and breathing air. This quantity has 

 been found by Hutchinson to vary in different individuals, 

 bearing a close relation to stature. The mean complemental 

 volume is 110 cubic inches. 



The complemental air is drawn upon whenever an effort 



1 We have not thought it worth while to enumerate the varied estimates found 

 in works on physiology, which are not based on extended experimental inquiry 

 26 



